The electromechanical integrated electrostatic harmonic drive is a new drive system invented by authors. The dynamic displacements of the flexible ring for the drive have important influence on operating performance of the drive system. In this paper, the three dimensional dynamic equations for the drive system are presented. The mode function equations and the frequency equation for the drive system are derived. The natural frequencies and dynamic displacements of the drive system are obtained. Using a finite element method analysis package, ANSYS , the natural frequencies and vibrating modes of the flexible ring for the drive system are simulated. The simulation results are compared to the analytical results above. The research is useful in design and manufacture of the drive system and can be used to design dynamic performance of the drive.